Association between fat mass index, fat‐free mass index and hemoglobin A1c in a Japanese population: The Tohoku Medical Megabank Community‐based Cohort Study

AIMS/INTRODUCTION: Fat mass and fat‐free mass affect glycated hemoglobin A1c (HbA1c) levels and blood glucose levels, respectively. The aim of the present study was to examine the association between the fat mass index and fat‐free mass index with HbA1c. MATERIALS AND METHODS: We carried out a cross‐sectional study that included 3,731 men and 9,191 women aged ≥20 years, living in Miyagi Prefecture, Japan, who were not treated for diabetes. The fat mass index and fat‐free mass index were calculated as fat mass and fat‐free mass divided by the height squared, respectively. The indices were classified into sex‐specific quartiles and combined into 16 groups. An analysis of covariance was used to assess associations between the combined fat mass index and fat‐free mass index with HbA1c adjusted for potential confounders. The linear trend test was carried out by stratifying the fat mass index and fat‐free mass index, entering the number as a continuous term in the regression model. RESULTS: In multivariable models, a higher fat mass index was related to higher HbA1c levels in men and women in all fat‐free mass index subgroups (P < 0.001 for linear trend). When we excluded the participants who had been identified as having diabetes, the fat‐free mass index was also related to higher HbA1c levels in most fat mass index subgroups (P < 0.05 for linear trend). CONCLUSIONS: Fat mass index was positively related to HbA1c levels. The fat‐free mass index was also related to HbA1c levels when we excluded participants who had been identified as having have diabetes.